Method of machining an elongated shaft

ABSTRACT

A METHOD AND APPARATUS ARE PROVIDED FOR STEADYING AN ELONGATED HORIZONTALLY DISPOSED ROTATING SHAFT AGAINST OSCILLATORY MOVEMENT DURING A TURNING OPERATION. IN THE APPARATUS DISCLOSED, DOWNWARD PRESSURE IS APPLIED AT SPACED POINTS ALONG THE SHAFT THROUGH SETS OF ROLLERS FORMED OF A VIBRATION-DAMPING MATERIAL.

- Feb. 9, 1971'. D. w. PEASLEY METHQDIOFI' MACHINING AN ELONGATED SHAFTFiled March 19, 1968 VI v mm R& i OA E w TE W V 3 mm A L G U 0 D 8 w I.mi x .1 i

United States Patent C 3,561,300 METHOD OF MACHINING AN ELONGATED SHAFTDouglas W. Peasley, 3114 S. Austin Road, Cicero, Ill. 60650 Filed Mar.19, 1968, Ser. No. 714,235 Int. Cl. B23b 3/00 U.S. Cl. 821 11 ClaimsABSTRACT OF THE DISCLOSURE A method and apparatus are provided forsteadying an elongated horizontally disposed rotating shaft againstoscillatory movement during a turning operation. In the apparatusdisclosed, downward pressure is applied at spaced points along the shaftthrough sets of rollers formed of a vibration-damping material.

The present invention relates generally to methods and apparatusemployed in the machining of elongated shafts. More particularly, theinvention relates to methods and apparatus for steadying elongatedshafts during a turning operation.

In the precision machining or turning of elongated shafts, both tubularand solid, it is necessary that the shaft rotate as smoothly as possibleabout a longitudinal axis. Two problems which must be overcome in such amachining operation are the tendency of the shaft to whip and thetendency of the shaft to vibrate. Both movements, as well as any othermovements'tending to cause periodic deviation of the rotational axisfrom a stationary nonfiuctuating condition, although not necessarily astraight line, will hereinafter be referred to as oscillatory movements.Whipping, which may be considered to be the tendency of the center ofmass of the shaft to orbit about the intended rotational axis of theshaft, is common in shafts of significant length, e.g., 14 to 16 feet,where the sheer weight of the shaft causes it to bow or sag at thecenter when it is supported solely at its ends. As the shaft is rotated,the displacement of the center of mass from the intended rotational axisis accentuated by centrifugal forces.

Vibrations within a rotating shaft can be accentuated by the forcesapplied to the shaft by the cutting tool and can also be accentuated byvibrations occurring within the immediate environment or within otherportions of the lathe and transmitted to the shaft.

There have been two general approaches to the problem of whipping andvibration and other oscillatory movements. A generally accepted approachis the provision of a device known either as a steady rest or as aroller rest. This device is fixed to the bed of the lathe and includesthree or four metallic rollers equally spaced around the periphery ofthe shaft and in engagement therewith. The rollers are supported forrotation about axes maintained as stationary as possible relative to theshaft so that, ideally, the shaft will be completely contained and canrotate only about a stationary axis.

The steady rest approach, although widely used, is not completelysatisfactory. 'In order for the rollers to be supported rigidly enoughand in precise relation to each other, it has been considered necessaryto mount them adjacent the inner surface of a solid ring which encirclesthe shaft. This makes it impossible to machine the shaft from one end tothe other in a single pass. Thus, it has been necessary to first mountthe shaft in the lathe and then while rotating the shaft at a relativelyslow speed, machine a narrow band at a location slightly to one side ofthe longitudinal mid-point of the shaft. The steady rest is then mountedon the lathe bed in encircling relation to the ice machined band withthe rollers 0f the steady rest in engagement with the band. The shaft ismachined at a somewhat higher speed from one end past the mid-point andup to the steady rest. To complete the machining operation, that is, tomachine the remaining half of the shaft, the shaft is removed from thelathe, reversed end for end, and re-mounted in the lathe with therecently machined portion of the shaft disposed within the steady rest.The remainder of the shaft is then machined.

A serious disadvantage in the use of the conventional steady rest is thetime delay caused by the necessity of halting the operation aftermachining only one-half the shaft, removing the shaft from the lathe,reversing it end for end, and again're-mounting it in the lathe for themachining of the remaining one-half. A second serious limitation is thefact that when the machining operation is interrupted and the shaftreversed end for end, the axis of rotation of the half first machined isnot co-linear with the axis of rotation of the second half, due possiblyto changes which take place within the shaft itself as stresses arerelieved by the machining operation. Frequently, therefore, it isnecessary to again reverse the shaft end for end and make a third andthen a fourth pass.

Moreover, the use of a steady rest does not eliminate vibrationscompletely and, accordingly, the shaft must be rotated at a relativelylow speed during the machining operation to prevent vibrations fromreaching an intolerable level. Finally, the use of a single steady restnecessarily leaves at least one-half of the shaft unsupported, eventhough the over-all length of the shaft being turned may be quite large.As the over-all length increases, the vibration problem becomes moreserious and the tendency for whipping to re-occur becomes more likely.However, the use of more than one steady rest compounds the problems anddelays necessitated by reversing the shaft end for end. The use of morethan one steady rest is therefore impractical. Hence, as the overalllength of the shaft increases, the practical speed of rotationdecreases.

A second approach to the problem of whipping and vibration is the use ofa so-called follower rest, a device which is similar in design to thesteady rest but is mounted on the tool holder carriage and movestherewith along the shaft. In theory, the follower rest steadies theshaft at the area in which the working occurs while the remainder of theshaft is free to whip or vibrate as the case may be. While the use of afollower rest permits a continuous pass along the length of the shaftwithout reversing the shaft end for end, as with the steady rest, itdoes not eliminate the whipping and vibration, making relatively lowspeeds of rotation and several cuts and finishing cuts necessary.

Accordingly, it is a principal object of the present invention toprovide an improved method and apparatus for machining an elongatedshaft.

Another object of the invention is to provide an improved method andapparatus for steadyin'g an elongated shaft during a machiningoperation.

Other objects and advantages of the invention will become apparent withreference to the following description and the accompanying drawing.

In the drawing:

FIG. 1 is an elevational view of a lathe incorporating a device showingvarious of the features of the invention;

FIG. 2 is a sectional end view taken along line 22 of FIG. 1; and

FIG. 3 is a diagrammatic view showing the application of forces to theshaft on the lathe shown in FIG. 1.

A pair of the apparatus 10 showing various of the features of thepresent invention is illustrated in the drawing. However, although twosuch apparatus are illustrated, only one will be described in detail, itbeing understood that the other is identical in construction to it.

The illustrated apparatus, which shows various of the structuralfeatures of the invention, is also adapted to be employed in thepractice of the method of the invention. Modified forms of theillustrated apparatus also fall within the scope of the invention, andcan also be employed in the practice of variations in the method of theinvention.

The apparatus is shown as mounted on a standard or conventional lathe 12having a head stock 14, a tail stock 16, and a bed 18. A carriage ismovable along the bed and carries a cutting or machining tool 22,represented diagrammatically in FIGS. 2 and 3. Supported between thehead stock 14 and the tail stock 16 is a work piece in the form of anelongated shaft 24 which may be a hollow tubular shaft, as illustratedin FIG. 2, or a solid shaft. It will be assumed that the shaft is longenough to present a problem of whipping and/or vibrating, i.e.,oscillatory movements, when it is rotated at a desired operationalspeed. The problems of oscillatory movement might also be expected in asolid shaft of similar diameter and somewhat greater length, or ineither a hollow or solid shaft of similar length but a significantlylesser diameter.

The apparatus 10 (FIG. 2) includes a bracket 26 which is suitably boltedto the rear of the lathe bed 18, i.e., that portion of the lathe bedopposite the carriage 20. Preferably, the lathe bed is provided with aplurality of accommodating sets of holes along its length so that thebracket can be mounted at various locations depending upon the length ofthe shaft being turned, as discussed in further detail herein. Othermounting means, such as a rail to which the bracket is clamped, could ofcourse also be employed without departing from the scope of theinvention. Conceivably, the bracket, or its equivalent, could also bemounted on the floor or wall, adjacent the lathe.

The bracket 26 defines a horizontal upwardly facing plateau on which ismounted a support 28, both the bracket and support being of heavy stockto enable them to withstand considerable force without significantdeformation. The support is a single integrated unit and includes a post30 and an arm 32 which extends at generally right angles to the post.The free end of the post, which in fact is the lower end, is flanged tofacilitate attachment thereof to the plateau of the bracket. Whensuitably mounted on the bracket by means of bolts or the like, the postextends generally vertically upwardly behind the shaft being tnr-ned andthe arm 32 extends forwardly above and in partially overhanging relationto the shaft. A threaded opening extends vertically through the arm 32above the axis of rotation of the shaft and receives a pressure screw 34provided with a pressure button 36 at its lower end and with a handle 38at its upper end. A hook 40 is pivotally mounted on one side of the armto engage a pin 42 on a lever 44, as hereinafter described.

The lever 44 is mounted on the post 30 for pivotable movement about ahorizontally disposed axis. The lever extends forwardly from the post 30beneath the arm 32 above and in overhanging relation to the axis ofrotation of the shaft and includes a flat upper surface engageable bythe button 36 of the pressure screw 34. The pin 42 projects laterallyfrom a side of the lever and is engaged by the hook when the lever islifted a sufiicient degree, thereby making it possible to maintain thelever in an out-of-the-way position for mounting and dismounting of aworkpiece.

Pivotally mounted adjacent the upper end of the lever 44 by means of apin 48 is a pair of generally triangular plates 50, the pin passingthrough one of the apexes of each of the plates. A roller 52 isrotatably mounted adjacent each of the remaining two apexes of theplates by means of roller shafts 54. Because of the orientation of theplates, the axes of rotation of the rollers are therefore locatedbeneath the lever 44. Each roller is formed to provide an outerperipheral portion of a vibration damping material such as natural orsynthetic rubber. In a preferred embodiment, the rollers are formed of amaterial sold under the trademark neoprene, are two inches in width attheir periphery, and have a durometer hardness of between and 100. Inaddition to the vibration-damping feature, a material such as neoprenedoes not mark the shaft at the area of engagement as do the metal rollsof the conventional roller rest. This feature is particularly importantwhere the finish of the shaft is critical.

In the use of the apparatus 10, the shaft 24 is mounted in the lathe inthe usual manner. During the mounting, the lever 44 is maintained in anout-of-the-way position by the hook 40 and pin 42. With the shaft inplace, the hook 40 is disengaged so that the rollers 52 rest upon theupper surface of the shaft. The screw 34 is then rotated by means of thehandle 38 to force the lever 44 downwardly and, in so doing, to forcethe rollers 52 into pressure engagement with the shaft. While the amountof force applied may vary depending upon the size of the shaft, in apreferred embodiment the force exerted by the two rollers of eachapparatus 10 is approximately 400 pounds. This force could of coursealso be created by an hydraulic system if desired.

In the illustrated embodiment, two apparatus 10 are illustrated for asingle shaft 24. In one practice of the invention, where a stainlesssteel tube with a 12-inch outer diameter and a length of 16 feet isbeing turned, it is helpful to employ two of the apparatus, one beinglocated approximately 5 feet from one end of the shaft and the otherbeing located approximately 5 feet from the opposite end, thus dividingthe shaft into three sections, each having a length equal toapproximately onethird the over-all length of the shaft. For shortershafts, a single apparatus may be adequate, while for longer shafts evena greater number of apparatus 10 may be advisable. The precise locationof the apparatus is not believed critical except that, insofar asvibrations of the shaft are concerned, it is preferable for theapparatus to be located at a point where the center of vibrational loopsor anti nodes occur rather than at points where nodes occur. Thus, forexample, if a single apparatus is used, it is preferable that it not belocated at the midpoint of the shaft.

It has been found that the use of the present apparatus in place of aconventional steady rest appreciably shortens the time required to turnthe shaft. For example, a hollow shaft 14 feet in length and 12 inchesin outer diameter formerly required 5 /2 hours to turn; through the useof the present method and apparatus, an identical shaft can be turned in1 /2 hours. It is not known precisely which of the features of theinvention are the most significant or whether, in fact, all the featurescontribute significantly. The apparatus 10, of course, makes it possibleto turn the shaft from one end to the other without interruption. Thus,it is not necessary to halt the operation and reverse the shaft end forend. This alone results in a considerable savings of time.

The working of the shaft end to end without interruption is madepossible by the fact that the apparatus 10 is capable of supporting theshaft without the use of a continuous ring which encircles the shaft, asin the conventional steady rest. That is, the cutting tool can actuallyoperate upon the area being engaged by the rollers of the apparatus 10without moving the apparatus or altering it in any way except perhaps toturn down the pressure screw slightly after the area engaged by therollers has been machined. This slight additional rotation of thepressure screw would compensate for the slight amount of materialremoved. However, even this has not been found to be necessary.

The ability of the apparatus 10 to maintain the shaft in place, i.e., tocause the shaft to rotate about a relatively fixed axis, is believed dueat least in part to the fact that the vertical components of the forcesapplied through the rollers deflect the shaft downwardly and that thisdeflection is maintained throughout the turning operation since therollers are not allowed to return to a nondeflecting position. Insofaras displacement in a vertical plane caused by oscillations of the shaftis concerned, the shaft can only be displaced downwardly a distanceequal to the difference between one half the normal oscillatorydisplacement and the deflection induced by the rollers. That is, if thenormal vertical oscillatory displacement is 10 mm. mm. above the averageaxis and 5 mm. below), and the deflection caused by the rollers is 4mm., the greatest possible oscillatory displacement is 1 mm. If,however, the deflection caused by the rollers exceeds one-half thenormal oscillatory displacement, i.e., 5 mm., there will be no verticaloscillatory displacement. Horizontal oscillatory displacement is, on theother hand, minimized by the counteracting lateral components of theforces exerted by the rollers. In FIG. 3, a simplified force diagram isshown. It will be noted that there is a lateral component of the forcesexerted by the two rollers in each of two opposite horizontaldirections. If each of these components exceeds the force tending todisplace the shaft in a direction opposite to it, there will be nolateral displacement and the shaft will be effectively contained forrotation about a stationary axis. Stated another way, if the forcesmaintaining the shaft against lateral displacement exceed the forcestending to cause such displacement, lateral or horizontal displacementwill not occur.

Thus, the vertical components of the forces applied by the rollers causea vertical deflection which prevents vertical displacement. Thehorizontal components of these forces do not cause deflection butcontain the shaft and prevent lateral displacement.

In the illustrated embodiment the two rollers of each apparatus arecircumferentially spaced from each other around the shaft on oppositesides of a vertical plane containing the axis of rotation of the shaftand are equidistant from that plane above the axis. This arrangement isbelieved preferable since the downward deflection is in the direction ofthe gravitational forces and, furthermore, does not interfere with theaction of the cutting tool when the cutting tool is located at a pointapproximately at the horizontal level of the axis. It would not bedesirable, of course, to deflect the shaft in a direction toward or awayfrom the cutting tool since this would result in a shaft which wouldeither be highly concave or highly crowned at its center. It isconceivable that the shaft could be deflected upwardly by placing therollers beneath the shaft and applying an upward force. However, this isthought to be less desirable since the chips cut from the shaft wouldtend to enter the nip between the shaft and roller. This would soondamage relatively soft rollers and, in some instances, might also damagethe surface of the shaft.

As has been pointed out, the triangular plate 50 is pivotably connectedto the lever 44 above the axis of rotation of the shaft. This permitsthe rollers to adjust slightly if, for example, the true center ofrotation is located slightly laterally of a point directly beneath thepin 48. In such an instance, the plate 50 can pivot slightly in onedirection to assure uniform application of pressure.

The use of composition rollers is believed helpful in minimizingvibrations. In a preferred embodiment, rollers having a durometerhardness of between and have been found to be satisfactory and arebelieved to damp vibrations within the shaft. Such damping rollers couldnot conveniently be employed with conventional steady rests or rollerrests since in neither device is pressure applied to the shaft by therollers; rather, the rollers merely contain the shaft. Deformablerollers, not under pressure, would not be capable of effectivelycontaining the shaft, but would give or deform in response tovibrations.

It also helps to employ more than one steadying device in the turning ofthe shaft since this shortens the effective length of the shaft beingturned. The use of two or more apparatus 10 is therefore believed tocontribute to the success of the invention. Previously, it was notpractical to use more than one conventional steady rest because of theinconvenience of reversing the shaft end for end. Ideally, a sufficientnumber of apparatus 10 are employed so as to divide the shaft intosections, none of which is sufficiently long to cause the section tovibrate at its resonant frequency at the desired rotational operationalspeeds of the shaft.

An improved method and apparatus have thus been described which permitrapid, more efficient turning of a shaft with minimal vibrations andwhipping but without loss of accuracy within the desired tolerances.

While one specific structural embodiment of an apparatus formed inaccordance with the present invention for practicing one form of methodfalling within the scope of the invention has been shown and described,it should be apparent that various modifications may be made in theapparatus and in the method of the invention without departing from thescope thereof.

Various of the features of the invention believed to be novel are setforth in the following claims.

What is claimed is:

1. A method of machining an elongated shaft having a tendency tooscillate during the machining operations, which method comprises:

(A) supporting the shaft adjacent its opposite ends for rotation aboutits longitudinal axis,

(B) effecting rotation of said shaft about said axis,

(C) deflecting the shaft in a plane of potential oscillatory movement,

(D) and effecting engagement between a machining tool and the shaftprogressively along a given line while exerting a force on the machiningtool in a given direction and while maintaining said deflection of saidshaft,

(1) the line of engagement between the machining tool and shaft beinggenerally parallel to the plane of deflection and lying in a planeparallel and in close proximity to a plane normal to the plane ofdeflection and containing the axis of rotation of the shaft,

(2) the direction of the force exerted on the machining tool beinggenerally normal to the plane of deflection.

2. A method in accordance with claim 1, wherein a section of the shaftis deflected to at least as great an extent as one-half the totaldisplacement of the section which the force causing the oscillationwould otherwise be capable of effecting in the plane of deflection.

3. A method in accordance with claim 1, wherein the deflection ismaintained by engaging the deflected shaft With means capable ofresisting movement by oscillationinducing forces tending to displace theshaft in a direction opposite to said direction of deflection.

4. A method in accordance with claim 1, wherein the shaft is furtherrestrained by engagement thereof by means capable of resisting movementby oscillation-inducing forces tending to displace the shaft in each oftwo opposite directions normal to said direction of deflection.

5. A method in accordance with claim 1, wherein deflection isaccomplished and maintained by engaging the shaft with a pair of rollersat points spaced from each other circumferentially around the shaft adistance no greater than one-fourth the circumference of the shaft atthe area of engagement, and applying a force to each of the rollersurging it in the direction of the axis of rotation of the shaft.

6. A method in accordance with claim 5, wherein the rollers engage theshaft above the axis of rotation thereof on opposite sides of a verticalplane containing the axis of rotation and in equally spaced relation tosaid plane.

7. A method in accordance with claim 1, wherein deflecting forces areapplied at each of two points spaced along the shaft, one of said pointsbeing located approximately midway between the longitudinal center ofthe shaft and one end and the other point being located approximatelymidway between the longitudinal center of the shaft and the oppositeend.

8. A method in accordance with claim 1, wherein a deflecting force isapplied to a suflicient number of points along the shaft so that themaximum distance between any point and the adjacent end of said shaft orany point and an adjacent point is less than the minimum length of shaftcapable of vibrating at its resonant frequency at the desiredoperational speed of rotation of the shaft.

9. A method of steadying an elongated horizontally disposed rotatingshaft against oscillatory movement during a turning operation, whichmethod comprises placing a pair of rollers in engagement with saidshaft, each of said rollers engaging said shaft at a point above theaxis of rotation of said shaft, the points of engagement of said shaftby said rollers being located on opposite sides of a vertical planecontaining the axis of rotation of the shaft and being equally spacedtherefrom, exerting a force on said shaft uniformly through said rollerseffective to deflect the shaft, and maintaining the rollers in theposition causing said deflection.

10. A method in accordance with claim 9, wherein said rollers are formedof a vibration-damping material.

11. A method in accordance with claim 9, wherein said points ofengagement of said rollers are spaced circumferentially from eachapproximately 45.

References Cited UNITED STATES PATENTS LEONIDAS VLACHOS, PrimaryExaminer US. Cl. X.R. 8238

